Experimentelle und numerische Untersuchung der 3D kurze Ermüdungsrisse zur Quantifizierung der Lebensdauerverbesserung durch Oberflächenverfestigung

• Applicant: Professor Dr.-Ing. Huang Yuan
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes
• Term: from 2011 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 203906638

• Final Report Year: 2015

Final Report Abstract

A cyclic cohesive zone model in analogy to the Roe-Sigmund model is introduced with XFEM to predict the fatigue crack growth behavior. The crack nucleation and growth can be described uniformly by the proposed damage evolution equation. The computations are examined by extensive experimental data performed within the frame of the present project. It is confirmed that the Paris region at different loading ratios can be reproduced by the cyclic cohesive model, only when the loading ratio is included into the damage evolution equation. Furthermore, numerical experiments confirm that the model cannot simulate fatigue crack propagation with severe plastification since the fatigue damage evolution is not coupled with the fracture damage explicitly, i.e. the low cycle fatigue crack growth cannot be predicted by the cohesive zone model. Such cohesive zone models cannot be used to predict fatigue crack growth in real structures. In order to generate reliable experimental data base for verifying cohesive zone models, fatigue tests have been conducted. The stainless steel SS2304 was taken for this purpose. CT specimens were used to identify basic model parameters and CTS specimens were applied for study fatigue crack propagation under mixed-mode loading conditions. Holed CTS specimens were tested for examining crack nucleation under different stress concentrations. We were especially interested in transition region with high crack growth rates between the regime II and regime III in the da/dN diagram. Based on the detailed experimental tests, a new cyclic cohesive zone model is proposed to predict both fracture and fatigue crack growth uniformly, i.e. for both low crack growth rate and high crack growth rate, up to elastic-plastic rupture. The fatigue damage evolution is coupled with fracture damage explicitly. The crack growth at Regime III is represented by the proposed model. The model parameters can be divided into two sets: monotonic model parameters and cyclic model parameters. The mixed mode fatigue crack growth is predicted by using the proposed cohesive zone model in combining with the maximum circumferential stress criterion. Fatigue crack propagation experiments have been conducted by using the compact tension shear (CTS) specimens made of SS 304 under the mode I condition and mixed mode I/II conditions. The computational results agree with experimental data of the stainless steel SS304, the monotonic cohesive parameters of the model are determined from the fracture tests and the cyclic damage parameters are obtained from the tensile fatigue tests. The present cyclic cohesive model provides a uniform description for both low rate as well as high rate of fatigue growth in the whole da/dN curve, more experimental results are still recommended to verify the numerical simulations systematically. With respect to fretting fatigue, nucleation of the fatigue crack is of importance. Detailed experiments on holed specimens have not given quantified results about correlation between fatigue crack nucleation angle and stress concentration. In all tests of holed specimens the crack nucleates following the maximum circumferential stress criterion. The main aim of the present project investigates fatigue crack propagation under LCF loading conditions. Based on the cohesive zone model concept the fretting fatigue can be resolved uniformly. The present work confirms that the fatigue crack can be predicted by the cohesive zone model properly in 2D specimens. However, 3D influence remains an open issue and needs to be investigated for damage tolerant design.

Publications

• An efficient nonlocal treatment for 3D damage modeling based on the background mesh concept. Proceeding of 19th European Conference on Fracture. 26-31, August, 2012. Kazan, Russia
  Huan Li, Xiaofei Pan and Huang Yuan
  
• Cohesive zone modelling of low cycle fatigue cracks in cracked and notched specimens. Fatigue & Fracture of Engineering Materials & Structures, 36:1246- 1257, 2013
  Huan Li and Huang Yuan
  
• Simulation of fracture and fatigue damage in stainless steel 304 using a cohesive zone model. Proceeding of 13th International Conference on Fracture. 16-21, June, 2013. Beijing, China
  Huan Li and Huang Yuan
  
• Computational and experimental investigation of elastoplastic cracks under monotonic and cyclic loading conditions. PhD Thesis, Department of Mechanical Engineering, University of Wuppertal, Germany. VDI Press, Düsseldorf, ISBN 978-3-18-334118-4, 2014
  Huan Li
  
• Modeling of mixed mode fatigue crack growth in stainless steel 304 using cohesive zone models. 46. Tagung des DVM-Arbeitskreises a Bruchvorgänge. 10-11, February, 2014. Kassel, Germany
  Huan Li, Xiaofei Pan and Huang Yuan
  
• A nonlocal treatment technique based on the backgroundcell concept for micro-mechanical damage modeling. Acta Mechanica, 226:1529- 1547, 2015
  Huan Li, Xiaofei Pan and Huang Yuan
  
• Assessment of low cycle fatigue crack growth under mixed-mode loading conditions by using a cohesive zone model. International Journal of Fatigue, 79:39-50, 2015
  Huan Li, Huang Yuan and Xiao Li
  
• Prediction of Low Cycle Fatigue Crack Growth under Mixed-mode Loading Conditions Using Cohesive Zone Models. Procedia Engineering, 99:1317-1322, 2015
  Huang Yuan, Huan Li and Xiao Li